An attorney for Bryan Pagliano said that he would "respectfully decline" a request to testify before two Senate committees, according to a letter provided to the Associated Press on Friday. Pagliano received an immunity deal from the Justice Department in early March in exchange for cooperating with the FBI's investigation into the issue.

Pagliano had previously refused to testify based on his Fifth Amendment right against self-incrimination. After the immunity deal was announced, Sen. Chuck Grassley, R-Iowa, and Sen. Ron Johnson, R-Wis., demanded that Pagliano testify before the Senate Judiciary Committee and Senate Homeland Security Committee, respectively, writing that there was "no longer reasonable cause" to believe his testimony could result in prosecution.

The response from Pagliano's attorney, which was dated March 11, argued otherwise, stating that "whatever agreement Mr. Pagliano may have reached with the Justice Department in no way constitutes a waiver of his Fifth Amendment rights."

Pagliano established the private server in Clinton's home in Chappaqua, N.Y., in 2009, unbeknownst to any of his superiors at the State Department. Clinton, in turned, granted him a political appointment at the department, an usual arrangement for an information technology aide.

The FBI has reportedly been seeking technical information about the server from Pagliano, in addition to physical evidence, such as photographs, that show when and where Clinton used devices in connection with the server.